This invention relates to anionic waterflood additive compositions and to their use to promote the recovery of secondary and tertiary oil from a petroliferous formation. In one aspect the invention relates to carbon dioxide saturated sulfonates having reduced adsorption characteristics and the use of such compositions to promote the recovery of secondary and tertiary oil from a petroliferous formation.
A large percentage of the oil in petroliferous strata is held within the rock of the strata by the surface forces between the rock, the oil, and the formation of water. As a result, a substantial portion of this oil usually remains in the rock even when wells traversing the strata are no longer productive. Various secondary recovery techniques, such as thermo recovery, gas injection, and water flooding, have been suggested for the recovery of this fixed oil which remains in the formation after it can no longer be produced by primary recovery methods. Of these secondary recovery techniques, waterflooding is quite commonly chosen, and a multitude of methods has been suggested for improving the efficiency and economy obtained from the practice. Such methods frequently include incorporation of a water-soluble surfactant in the waterflood. Typical surfactants which have been proposed for this purpose include alkyl pyridinium salts, sodium lauryl sulfate, sulfonates, glycosides, sodium oleates, quaternary ammonium salts, and the like. The use of such surfactants has arisen because it is widely recognized that a low interfacial tension between the surfactant floodwater and the reservoir crude is essential to the improvement of recovery efficiencies.
Recently it has been proposed that nonionic surfactant solutions, such as a polyoxyethylene-polyoxypropylene copolymer containing solution be injected into the formation through a first of at least two well bores to thereby displace the hydrocarbons towards a second well bore. The nonionic surfactant flood is then followed by the injection of a slug of aqueous caustic into the formation through the first well bore to displace the hydrocarbon and the surfactant toward the second bore. The caustic slug has a basicity at least 1.5 pH units greater than that of the native formation water.
More recently it has been proposed to overbase petroleum derived sulfonates, synthetically derived sulfonates of mixtures thereof to provide an overbased sulfonate waterflood additive having improved residual oil recovering properties. However, in the use of sulfonates, especially synthetically produced sulfonates, problems are often encountered due to the absorption of the sulfonate onto the petroliferous formation. Thus, it is desirable to provide a waterflood additive composition which reduces the amount of surfactant component absorbed on the petroliferous formation.
According to the present invention, anionic waterflood additive compositions have been developed which comprise a carbon dioxide saturated sulfonate having an equivalent weight of about 300 to about 600. Such carbon dioxide saturated sulfonates, when injected into a petroliferous formation, substantially reduce the amount of sulfonate adsorbed on the formation during the waterflood process. Further, any suitable sulfonate having an equivalent weight of from about 300 to about 600, or blends thereof, can be saturated with carbon dioxide and thereafter employed as the waterflood additive composition of the present invention. The sulfonates, which will be more fully described herein, can be obtained by the sulfonation of various refinery streams and synthetic alkylates. Further, the sulfonates can be either neutralized sulfonates or overbased sulfonates.